Background. The purpose of this study was to analyze the causes of flap compromise and failure in head and neck free flap reconstruction.Methods. We retrospectively reviewed 1310 free flap reconstructions for head and neck defects performed between July 1995 and June 2006.Results. Forty-nine cases of flap compromise due to vascular obstruction (3.7%) were identified, and 27 flaps were lost (2%). Arterial occlusions occurred in 12 flaps, with a salvage rate of 33%. Eight flaps failed within the first 24 hours, and only 1 of these was salvageable. Five of the 8 flaps had intraoperative thrombosis due to technical difficulties. Venous occlusions occurred in 31 flaps, with a salvage rate of 58%. Twenty-two venous occlusions occurred within the first 72 hours. The main reason for venous failure was mechanical obstruction due to compression, twisting, kinking, or stretching of the vein. The most common cause of late failures (after 7 days) was unrecognized failure of a buried flap owing to the lack of reliable monitoring. Overall, there was no correlation between surgeon experience and flap failure, but the flap failure rate was lower in surgeons who had performed more than 70 free flap procedures.Conclusion. Precise surgical techniques, avoidance of mechanical obstruction, and better monitoring of buried flaps may further improve the success rate of free tissue transfer in complex head and neck reconstruction. Free flap reconstruction has become an integral part of the multidisciplinary care of head and neck cancers in most major medical centers. The success rates for microsurgical procedures have greatly improved over the past few decades. Many centers have reported free flap success rates greater than 96%, and in some expert hands, close to 99%, 1-9 making this operation 1 of the most reliable procedures in reconstructive surgery. 1 However, flap crises and failures do occur occasionally, and most reports seem to show that free flap failure occurs more frequently in head and neck reconstruction than in breast reconstruction. 1,5,7,8 Early reports suggested that operator experience was the most important factor responsible for the success of free flap reconstruction. [1][2][3][4][5] For example, the free flap success rate of 1 surgeon improved from about 70% in early cases to greater than 96% in later cases. [1][2][3] This may reflect the early self-learning and trial and error experience. However, with current well-established microsurgery centers, standards, and training, many